You have here a split-cycle engine, which has been around, sometimes successfully, for over 100 years. But it's never stuck because its inherently less thermodynamically efficient (it also involves a multiple factor for friction loss, but that's less of an issue). Those that have worked have done so, for the most part, because racing rules allow a beneficial calculation in engine cylinder volume -- sometimes because they've allowed an effective supercharging effect due to relative cylinder volumes, without incurring a volume penalty.
But split-cycle engines transfer unburned, compressed fuel-air mixture from the compression cylinder to the combustion/power cylinder, directly. The only thermodynamic loss is the heat of compression lost to the compression cylinder and the between-cylinder passage. The fuel is burned conventionally in the combustion/power cylinder.
In your engine, you're burning the fuel in a separate, between-cylinders combustion chamber. You've greatly increased the wall area exposed to combustion heat, which necessarily involves a heat loss -- something like the heat loss that occurs in a flathead engine, with its attendant large combustion-chamber surface area. There's a very large thermodynamic inefficiency inherent in that design. How do you reconcile that?
I recognize that your new relative cyinder volumes can, potentially, give you an Atkinson-cycle effect that could improve thermodynamic efficiency. But the margins gained with the Atkinson cycle are fairly small; the losses due to increased combustion-chamber surface area are large.
Anyway, 'glad you stopped around. Your engine has provoked a lot of interesting discussion. d8-)
I agree that we have increased thermal losses due to the increased surface area over a conventional engine and we also have losses from compressing our fresh air volume into the combustion chamber and again we have losses when we open our combustion chamber to the power piston.
We have minimized the thermal losses in our combustion chamber by using a water based ceramic coating that we spray on our racing pistons and in our combustion chambers. This coating not only resist heat transfer it also reflects the heat back into the combustion chamber.
We have minimized flow losses as much as possible by optimizing our port size, shape and timing. Our intake port has a constant uninterrupted flow and due to the centrifugal effect of the rotating pistons we are able to delay the closing of the intake port. This allows us to use a smaller intake piston which helps to reduce ring and skirt drag.
In a conventional engine it is estimated that 30 percent of lost efficiency is from unused combustion being wasted through exhaust. This is a very substantial amount of wasted energy.
An efficient car engine is only about 33 percent efficient. If you could create an engine that was even a few percent higher it would be huge. To do this one of our goals was to try and recover some of the unused exhaust energy.
In a conventional Otto cycle the sound you hear from the exhaust is not the fuel being combusted, it is the exhaust valve being opened approximately 40 degrees before BDC while there is several hundreds of pounds of pressure still in the cylinder. Because they were not able to use this pressure for power they have to open the exhaust valve early to try and get rid of it so they don't have to work against it when the piston starts to travel back to TDC.
Another waste is the fact that you have to completely fill and completely empty the combustion chamber on every cycle. This is why using a higher compression ratio will give you better efficiency.
A 9 to 1 engine loses 1/9 of its energy just filling and emptying the combustion chamber.
A 12 to 1 only loses 1/12 to its combustion chamber.
Some other losses are from firing as much as 40 degrees BTDC and expansion BTDC from the residual heat from the previous power stroke heating the cool air during the intake and compression stroke.
In the DRE we have been able to change how the combustion pressure is distributed and used.
By using a split cycle we are able to keep our intake cylinder relatively cool and our combustion chamber and power cylinder are able to stay relatively hot.
This means that during our intake and compression strokes we are not working against pre expanding air from residual heat from a combustion and power cycle. We also do not ignite our fuel mixture until after TDC of the compression stroke. Our engine is not trying to run backwards.
Two things happen in the combustion chamber before the power stroke starts. First the cool air is able to absorb some of the heat that was left over from the previous combustion. This allows us to use leftover heat in a positive direction. Second is we allow the flame front to propagate for 60 degrees before it is open to the power stroke. This means we have nearly 100 percent of our available energy ready to use at TDC of our power stroke.
We open the combustion chamber to the power piston at TDC but only for about 100 degrees of rotation. And because we are using larger power pistons, which allows us to over expand, when our power pistons reaches BDC the net pressure is near zero which means we used as much of our combustion pressure for work as possible.
The other huge efficiency gain is that when we closed off the combustion chamber to the power stroke it left the unused combustion pressure and heat in the combustion chamber and did not dump it out of the exhaust. We get to use this toward the next power stroke.
So to maintain our necessary power level we do not have to start from zero on every cycle, we just need to add enough air and fuel to the residual pressure that was left in the combustion chamber to make up the difference of what was used for the 100 degrees of rotation that the combustion chamber was open to the power stroke.
Also our rotary layout cuts down on windage because we do not have a crank traveling through oil and air. We also do not experience the pressure/vacuum wave that is formed under a reciprocating piston. We also do not lose the estimated four percent of efficiency that is lost to opening and closing the valves of a cylinder head.
Our combustion temperatures are lower which helps with NoX and our longer burn duration helps with hydrocarbon emissions.
I hope this helps explain our engine a little better. We are close to finishing another prototype, maybe late July. We feel this one might be the first to make it off of the dyno and into a car.
I was 18 years old when I first started trying to build a better engine, I am now 46. I am glad this is just an expensive hobby because if I was trying to make a living off of it I would have starved by now.
Wow, there is so much thermodynamic engineering going on there that I couldn't ask enough questions to sort it all out.
But there is one that really intrigues me: After you close the intake valve to a power cylinder, how much pressure is left in the combustion chamber? I just mean in relative terms, not pounds per square inch.
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